A Directory Server backend provides a repository for storing data and a set of logic for interacting with that data. A backend will typically contain some kind of database and may maintain a set of LDAP Indexes that allows the backend to quickly locate entries for various operations. All backends will have the following qualities:

A backend ID, which uniquely identifies that backend among all other backends in the server.

A set of one or more base DNs that indicate the data that the backend holds.

A writability mode, which indicates whether the backend will accept write operations.

The logic provided by the backend includes:

A method for determining whether a given entry exists, based on its DN